The nose cone of an aircraft, rocket, missile, etc. typically includes a radome that houses a radar system or other similar communication system of the aircraft, rocket, missile, etc. During operation of the aircraft, rocket, missile, etc., the radome is subjected to high speed that produces a high temperature in the material of the radome. This is particularly true in radomes on the tips of rockets and missiles.
High temperature advanced rocket and missile radomes are usually made out of monolithic ceramic materials. Examples of these monolithic ceramic materials include glass ceramic (Pyroceram® by Corning Incorporated), silicon nitride (Ceralloy® by Ceradyne, Inc.), and fused silica. These materials have a low dielectric constant for good electrical transmission. The radomes are typically constructed with a truncated cone configuration with an apex opening at the top of the cone configuration and a base opening at the bottom of the cone configuration. The radome has an interior volume that houses a radar system.
A tip of the radome is typically constructed separate from the radome. One reason for this is that the ceramic material of the radome shrinks during construction of the radome. The radome needs to have an exact cross-sectional dimension for good electrical transmission and predictions of the radar system, as well as a smooth exterior surface for aerodynamics. This requires that the radome be centered, and the exterior surface of the radome be machined and polished on a lathe. Forming the radome with an integral tip makes these manufacturing steps impractical. Additionally, forming the radome of a monolithic ceramic material with an integral tip produces a radome with a brittle monolithic ceramic at the tip. If the tip gets hit by direct impact from an object in flight, even from rain, it could cause a catastrophic failure of the tip and the radome.
High speed ceramic radomes are typically constructed using a separate metal tip. The metal tip improves impact resistance and reduces the likelihood of the monolithic ceramic material of the radome catastrophically failing during use. However, using a metal tip on the monolithic ceramic material of the radome creates a number of problems. The metal tip blocks the transmission of signals from the radar system and reflects or scatters the signals of the radar system, producing a large blind spot that reduces the performance of the radar system.
Additionally, the coefficient of thermal expansion of the metal tip is higher than the coefficient of thermal expansion of the monolithic ceramic materials used to construct the radome. This makes it difficult to create a hermetic seal between the metal tip and the ceramic radome that is necessary to retain a controlled environment in the interior volume of the radome to protect the radar system components. Over time, the coefficient of thermal expansion difference between the metal tip and the brittle ceramic radome produces microcracks in the monolithic ceramic material of the radome causing the seal between the metal tip and the radome to leak and also causing the metal tip to separate from the ceramic radome.
The use of a separate monolithic ceramic tip attached to the monolithic ceramic radome is also problematic. The brittle nature of the monolithic ceramic tip which could cause catastrophic failure of the tip on impact with objects, even rain. It is also difficult to securely attach a separate monolithic ceramic tip to a brittle ceramic radome.